Not every resource you’re looking for in Monster Hunter Rise comes off of a monster you have to defeat. There are plenty of plants and smaller animals that have essential items that you need to craft helpful tools and equipment during your hunts. There are some items you need to for items, and there are some that will be requested by citizens of Kamura Village who need your help. There are some characters who will request you locate Raftshells or Bedshells. You can find these items in the same location, in the same region of the game.
You first need to travel to the Frost Islands. It’s the second area you unlock in the game. You won’t have to venture too far off the beaten path to find these resources. The Raftshells and Bedshells appear at the Oyster Bed locations in the Frost Islands. These gathering locations are scattered all over the water region. A majority of them are in the upper area, with a single one in the underground area. You’re better off focusing on the locations on the top section of the Frost Islands region.
These are all of the locations you find Oyster Beds to farm Raftshells and Bedshells.
When starting at your main camp, you swing down to the right side and make your way to region 4 to scoop up those first ones. Most of the Oyster Beds are hidden in the watery areas at the center, which you need to use a wirebug to access. They are all in the water and have a distinct yellow highlight to them, making them quick to find.